How to change the Row Definition in grid?

<grid>
           <grid.columndefinitions>
               <columndefinition width="250" />
               <columndefinition width="*" />
               <columndefinition width="Auto" />
           </grid.columndefinitions>
           <grid>
               <grid.rowdefinitions>
                   <rowdefinition height="150" />
                   <rowdefinition height="*" />
                   <rowdefinition height="Auto" />
               </grid.rowdefinitions>
               <textblock x:name="tb" grid.row="0" text="Hello" height="50" xmlns:x="#unknown"></textblock>
               <textblock x:name="tb2" grid.row="2" text="Hello2" height="50" xmlns:x="#unknown"></textblock>
           </grid>
       </grid>
       <Button Content="change" Click="Button_Click"/>

private void Button_Click(object sender, RoutedEventArgs e)
     {
        // string s = "Hello";
         Grid.SetRow(tb, 1);
     }